Strength Training Improves Nervous System Speed
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Aagaard et al. (2002). Increased rate of force development and neural drive of human skeletal muscle following resistance training. Journal of Applied Physiology, 93, 1318-1326.
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>Rate of force development (RFD) is how rapidly muscular force can be generated. It is the most important nervous system adaptation for athletes trying to improve “explosive” strength (i.e., power and speed).
>RFD is important for athletes because fast actions in sports like jumping, sprinting, and quick changes of direction (e.g., agility) involve short ground contact times (GCT) that require high forces to be generated rapidly. (This is similarly important for throwing and striking sports).
>Early-phase RFD is usually defined as the first 50-100 milliseconds of muscular contraction and is considered highly valuable because elite-level sprinting involves ground contact times that are less than 150 milliseconds.
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>15 untrained males were selected, tested, and retested for measures of RFD after 14 weeks of heavy resistance training (HRT) which included hack squats, leg presses, knee extensions, hamstring curls, and calf raises performed as heavy as 4-6 repetition maximums.
>HRT improved RFD at all measured time intervals: 30, 50, 100, and 200 milliseconds.
>HRT shifted/improved the entire force-time curve from start to finish.
>Additionally, there were improvements in neural drive (efferent motor outflow) and impulse (time-integrated force) following the HRT program.
>While muscle size, architecture, and fiber-type all influence RFD, the improvements created in this short-term training program were concluded to be primarily from increases in neural drive.
>Improved neural drive comes from the nervous system’s increased ability to send stronger signals to the recruited motor units (muscles).
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Take-Home:
>Fast, “explosive” resistance training is not required to increase rate of force development, the hallmark nervous system quality that power-focused training aims to improve.
>Despite heavy lifting being performed slowly--taking entire seconds (1,000’s of milliseconds)--improvements are made in the nervous system across the entire muscular contraction timeline and even during early-phase rate of force development (as quick as 30 milliseconds).
>Heavy resistance training is highly useful for multiple sports performance outcomes. Beyond hypertrophy (muscular growth), strength, and mobility, it is a key factor in power (“explosiveness”) and speed development.